By all means hunt in the rain. I have gotten more than a few deer in sub-optimal conditions. I took a small buck last week in high winds. Once a I got a "double" in the rain. Two deer (I had tags for both) in about two minutes in heavy rain - and better yet, I ran into the first one 10 seconds after I left the truck and the other as I turned to put away my rifle.

Unless you can hunt in your living room, you can't get a deer if you don't go out.